1. Field of the Invention
The present invention relates to a filter module.
2. Description of the Related Art
These days, in communication services provided by, for example, cellular phones, certain measures for an increased number of subscribers are being taken, global roaming enabling the worldwide use of communication services is being developed, the communication quality is being improved, and various contents being transmitted are becoming larger. In order to deal with such communication services, it is necessary that communication devices, such as cellular phones, support multiple bands and multiple systems. Accordingly, in a communication device which supports multiple bands or multiple systems, a plurality of interstage filters or wave splitters are mounted on an RF (Radio Frequency) circuit. That is, interstage filters or wave splitters corresponding to individual bands or individual communication systems are mounted on a communication device.
While the number of interstage filters or wave splitters mounted on an RF circuit is increasing, it is still desirable to reduce the size of a communication device. Accordingly, in order to reduce the size of an RF circuit, a study is being made to mount, on an RF circuit, a filter module constituted by interstage filters, wave splitters, and a plurality of matching devices corresponding to individual bands or individual communication systems. In Japanese Unexamined Patent Application Publication No. 2010-45563, a duplexer module, which is one type of filter module, is disclosed.
FIG. 17 is a schematic plan view of a duplexer module 100 disclosed in Japanese Unexamined Patent Application Publication No. 2010-45563. The duplexer module 100 includes a mount board 101 and first and second duplexers 102 and 103. The first and second duplexers 102 and 103 are mounted on the front surface of the mount board 101. The first and second duplexers 102 and 103 each include an antenna terminal, a transmission terminal, and reception terminals. The mount board 101 includes first and second antenna terminal electrodes, first and second transmission terminal electrodes, and first and second reception terminal electrodes. The first and second antenna terminal electrodes, the first and second transmission terminal electrodes, and the first and second reception terminal electrodes are formed on the back surface of the mount board 101.
The antenna terminal of the first duplexer 102 is connected to the first antenna terminal electrode of the mount board 101. The transmission terminal of the first duplexer 102 is connected to the first transmission terminal electrode of the mount board 101. The reception terminals of the first duplexer 102 are connected to the first reception terminal electrodes of the mount board 101. The antenna terminal of the second duplexer 103 is connected to the second antenna terminal electrode of the mount board 101. The transmission terminal of the second duplexer 103 is connected to the second transmission terminal electrode of the mount board 101. The reception terminals of the second duplexer 103 are connected to the second reception terminal electrodes of the mount board 101.
In order to support a case in which an RFIC of an RF circuit is a balanced input type, a reception filter of the first duplexer 102 is constituted by a longitudinally coupled resonator-type surface acoustic wave filter having a balanced-unbalanced transforming function. That is, the duplexer module 100 is a balanced filter module. Accordingly, the reception terminals of the first duplexer 102 are constituted by a pair of terminals, which are first and second balanced terminals. The first reception terminal electrodes of the mount board 101 are also constituted by a pair of terminal electrodes, which are first and second balanced terminal electrodes. Accordingly, a balanced signal is output from the first reception terminal electrodes of the mount board 101.
In the first duplexer 102, phase balance characteristics of reception signals output from the reception terminals are set to be around 0° in a passband of the reception filter and a passband of a transmission filter.
In the duplexer module 100 configured as described above, the phase balance characteristics of reception signals output from the first reception terminal electrodes of the mount board 101 may become deteriorated.